1. Field of Invention
This invention relates to an apparatus and method for displaying the lightning rate of activity and location from the observers.
2. Description of Prior Art
Thunder storms create great dangers particularly to air travel due to the turbulence and electrical activity (lightning). Pilots of aircraft need to track, predicted and avoided thunder storms. The electrical signals generated by thunderstorms vary greatly during the life of the thunderstorm. During the early stages of building thunderstorms, the number of electrical signals will increase. This is the stage of high turbulence. The number of electrical signals generated during the mature stage is also very high as is the ending stage of a thunderstorm. Weak storm fronts with little turbulence generate electrical signals but with very less frequent rate. The detection, recognition, accurate measurement and analysis of these electrical signals provide a basis for storm tracking, avoidance, etc.
Lightning flashes are composed of a series of high current lightning strokes, each stroke being proceeded by a lower current discharge called a leader. The duration of electrical activity associated with a lightning stroke varies but in many instances last as much as a hundred microseconds. The initial rise time of electrical signals associated with a lightning stroke almost never exceeds five microseconds. Following the first peak of the electrical signals of a lightning stroke, lesser signals of sub-microsecond duration but with fast rise times (of five microseconds or less) will occur. Several lightning detection systems have been created-for example, in U.S. Pat. No. 4,422,037 (1983), U.S. Pat. No. 4,672,305 (1987) both to Coleman, U.S. Pat. No. 4,639,666 (1987) to Strosser et al., U.S. Pat. No. 4,684,951 (1987) to Baumer, U.S. Pat. No. 4,803,421 (1989) and U.S. Pat. No. 4,873,483 (1989) both to Ostrander, U.S. Pat. No. 4,831,362 (1989) to Tsaprazis, U.S. Pat. No. 4,801,942 (1989), U.S. Pat. No. 4,972,195 (1990), and U.S. Pat. No. 5,057,820 (1991) all to Markson et al., U.S. Pat. No. 5,168,212 (1992) to Byerley, III et al., U.S. Pat. No. 5,263,368 (1993) to Breitmeier et al., U.S. Pat. No. 5,295,071 (1994) to Kuzma et al., U.S. Pat. No. 5,303,152 (1994) to Moses et al, U.S. Pat. No. 5,295,072 (1994) to Stevens, Jr. et al, U.S. Pat. Nos. 5,245,274, 5,408,175 (1995), U.S. Pat. No. 5,500,602 (1996), U.S. Pat. No. 5,502,371 (1996), U.S. Pat. No. 5,504,421 (1996), and U.S. Pat. No. 5,500,586 (1996) all to Youngqvist, U.S. Pat. No. 5,396,220 (1995) to Markson et al, U.S. Pat. No. 5,528,494 (1996) and U.S. Pat. No. 5,537,318 (1996) both to Moses, U.S. Pat. No. 5,441,501 (1996) to Shaver et al, U.S. Pat. No. 5,610,813 (1997) to Greenwald, U.S. Pat. No. 5,699,245 (1997) to Herold. These lightning detection apparatus determine range and bearing to storms using the frequency components emanating from lightning. These apparatuses suffer from a number of disadvantages:
1. The installation of these systems in aircraft requires locating the system away from low frequency (noises area) generators such as deicing equipment and 400 hertz power supply connections. PA1 2. Calibrating these systems to minimize aircraft effects and noise sources. PA1 3. The displaying of the rate of lightning activity over a predetermined time interval is not provided. PA1 1. Preliminary Discharge PA1 2. Dart Leaders PA1 3. Stroke(s) PA1 1. A lightning detection system whose installation is convenient and not susceptible to aircraft low frequency noise; PA1 2. A lightning detection system with increase range detection; PA1 3. A lightning detection system with increase sensitivity to displaying the rate of lightning.
Consumers installing the apparatus on aircraft have problems finding a location on the aircraft with low aircraft noise at the lightning frequency chosen by the apparatus. There are a limited number of locations available to the consumer to install lightning hardware antennas. The ability to move the antenna to minimize aircraft noise is costly and most cases prohibited, For example, in the U.S. Pat. No. 3,715,660, (Ruhnke) based on the ratio of signals representing the magnetic and electric field associated with the discharge. The determination of the direction of the discharge is not made. In addition, U.S. Pat. No. 4,422,037 (Coleman) and companion patent (U.S. Pat. No. 4,672,305) discloses a storm mapping system which determines range based on the ratio of electromagnetic fields measured at two set frequencies and comparing the obtained values to strikes occurring in three ranges near field, mid field and far field. These apparatuses range accuracy increased by decreasing the measured lightning frequency. Unfortunately, the aircraft power systems also work at lower frequencies. The apparatus ability to detect lightning at ranges to 100 miles was compromised. The consumer objected to this reduced range setting. Further, an apparatus (U.S. Pat. No. 4,873,483 and companion U.S. Pat. No. 4,803,421 (Ostrander)) determines the range to the lightning strike based on the ratio of integrated electromagnetic signals. The electromagnetic fields are associated to signals received by a narrow band and a wide band filter. Each pulse is further classified by the pulse width of the lightning discharge to isolates the far field, mid field and near field signals. As with the prior inventions, this apparatus measured the lightning over a wide frequency range. Thus the same potential for detecting aircraft noise caused false targets to be displayed. No display of lightning rate is provided.
Inventors have created apparatuses to detect the aircraft noise and minimize displaying false targets. For example, the U.S. Pat. No. 5,295,072 (Stevens) and U.S. Pat. No. 5,303,152 incorporates a number of the features included in the previously discussed patents. As set forth, the range and bearing is determined by taking many samples of the lightning signals over a period of time to determine the frequency signature. A group of filters are used to determine the frequency signature. Range and bearing is determined by applying a set of weights to each filter output. Further, the pulse width is used to classify the lightning strikes into three types to set the weight values. Although these apparatuses incorporated software algorithms to eliminate aircraft noise and false targets, the consumers still complain of false targets and confusion on the lightning storm location. No display of lightning rate is provided.
U.S. Pat. No. 5,500,586 (Youngquist), and companion U.S. Pat. Nos. 5,504,421 and 5,500,602 (Youngquist) incorporate a number of the previously discussed features. The storm monitoring apparatus orients the magnetic fields at an angle of 45 degrees to the heading axis of an aircraft and determines to range and bearing by evaluating at a high rate the frequency or spectrum of the lightning signal. This apparatus does not address the noise aircraft installation problem.
U.S. Pat. No. 4,023,408 discloses a storm mapping system that detects electrical activity caused by weather phenomenon such as lightning strokes. The system is intended to operate on the far field (or radiation field) pattern generated by the lightning stroke. According to the disclosed, the far field pattern is characterized mainly by a low frequency spectrum with maximum amplitude signals occurring between seven and seventy three kilohertz (kHz). A trio of antenna sensors, an electric field antenna and two-crossed magnetic field antennas, are used and each is connected to a tuned receiver on a center frequency of fifty kHz. The crossed loop magnetic field antennas are used to locate the lightning signals in azimuth angle by comparing the relative magnitude of the signals induced in the cross loop sensors to the electric field antenna in a conventional manner. The magnetic field signals are time correlated with the electric field signals before integration. This provides some measure of avoiding unwanted noise like signals. Integration of the correlated signals is formed for 0.5 milliseconds but only after the vector sum of the magnetic field sensor signals is found to exceed a predetermined threshold value. The algebraic sum of the magnetic field sensor signals is amplified and then squared. This signal is used to divide the integrator output signals thereby reducing the magnitude of larger correlated integrated signals below the magnitude of smaller ones. These inverted signals then drive a display such as a CRT display to show larger signals closer to the observation point and smaller signals farther away.
This system has been used on aircraft and appears to work well, but it depends heavily on the magnitude of correlated electric and magnetic field signals to provide a measure of the range of the signal from the observation point of the equipment. Accordingly, the accuracy of range estimates may be affected by the variation in the severity of the thunderstorms. Also, some of the detailed characteristics of lightning stroke signals are not utilized to discriminate between interfering signals and true lightning electrical signals. The rate of lightning activity over a predetermined time is not provided.